Generally, a basic structure of a thin film transistor liquid crystal display (TFT-LCD) comprises an array substrate, a color filter substrate and a liquid crystal layer arranged between the array substrate and the color filter substrate. The display device also comprises a pixel electrode and a common electrode for controlling the deflection of the liquid crystal molecules. In the TFT-LCD, the intensity of light can be controlled by controlling the deflection of the crystal liquid molecules, then color images display can be realized through filtration to the light by the color filter substrate. For example, the color filter substrate comprises a black matrix and color resin to display color. The array substrate and/or the color filter substrate is/are a display substrate.
Generally, in a producing process, a display substrate motherboard including a plurality of display substrates can be manufactured on one motherboard substrate to enhance productivity. After an upper display substrate motherboard and a lower display substrate motherboard (for example, an array substrate motherboard and a color filter substrate motherboard) are assembled, the assembled panel motherboard is cut into a plurality of small crystal liquid display panels.
In the process of manufacturing a display substrate, segment differences will be produced due to thickness differences of various layers and manufacturing sequence differences of various layers. In the cell assembling process, the surface of the display substrate is required to have a certain degree of flatness to avoid poor alignment of the coated alignment layers in the uneven regions to generate rubbing mura, so as to avoid impacting the display quality of the crystal display panel. It is necessary to measure and monitor different kinds of segment differences in the process of manufacturing display substrates.